Soft contact lenses can generally be classified into two groups: conventional hydrogel contact lenses and silicone hydrogel contact lenses. Conventional hydrogel lenses are typically formed from hydrophilic polymers and copolymers such as those containing repeating units from hydroxyethyl methylacrylate (“HEMA”) and methacrylic acid (“MAA”).
Silicone hydrogel contact lenses offer an advantage over conventional hydrogel contact lenses in that they improve oxygen permeability, which improves oxygen availability to the cornea.
The incorporation of sulfonic acid-containing components into polymers used for both conventional and silicone hydrogel contact lenses provides hydrophilicity to the lenses, resulting in lenses having high water content. 2-Acrylamido-2-methylpropane sulfonic acid (“AMPS”) is a sulfonic acid-containing monomer that has been incorporated into conventional hydrogel lenses. See, e.g., U.S. Pat. Nos. 5,451,617 and 5,011,275 and U.S. Patent Application No. 2008/0114123. Depending on the overall mixtures of monomers being used and the amount of sulfonic acid functionality desired, sulfonic acid-containing monomers may not always be soluble in a reactive monomer mixture.
With respect to silicone hydrogels, the AMPS monomer is not very soluble, which results in a hazy mixture. Methods of incorporating AMPS or other sulfonic acid-containing components in a silicone polymer/hydrogel were previously discussed by commonly assigned U.S. Patent Appln. Pub. No. 2013/0184372 (Reboul), which disclosed silicone polymers comprising a sulfonic acid component formed from reactive components comprising (i) at least one silicone component and (ii) at least one sulfonic acid-containing component, wherein the sulfonic acid-containing component is comprised of a non-polymerizable, hydrophobic cation and a polymerizable sulfonic acid. Such silicone polymers in turn can be used to manufacture silicone hydrogel contact lens having anionic properties and the benefits therefrom. The previous use of non-polymerizable, hydrophobic cations such as tripentylamine (TPA) to deliver polymerizable sulfonic acid as salts desirably gets rid of haze from the reactive monomer mixture, but removal of the cations after the silicone hydrogel contact lenses are made is necessary.
There is a need to provide chemistries to continue having clear reactive monomer mixtures while also providing efficient ways to remove any cations.